In order to increase data areas for writing user data in a magnetic disk device, a method has been employed by which to divide a servo pattern into a plurality of zones from inner periphery to outer periphery of a magnetic disk and set frequency for writing the servo pattern (reference frequency) in zone on the outer peripheral side to be higher than that in zone on the inner peripheral side (zone servo technique). According to zone servo technique, void regions of specific width with no user data written are provided in the vicinities of zone boundaries so that the servo pattern can be surely switched between the zones.